Negative evidence in language acquisition*

Cognition, 46 (1993) 53-85

Negative evidence in language acquisition*

Gary F. Marcus Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Received February 7, 1992, final version accepted July 2, 1992

Abstract

Marcus, G.F., 1993. Negative evidence in language acquisition. Cognition, 46: 53-85

Whether children require “negative evidence” (i.e., information about which strings of words are not grammatical sentences) to eliminate their ungrammatical utterances is a central question in language acquisition because, lacking negative evidence, a child would require internal mechanisms to unlearn grammatical errors. Several recent studies argue that parents provide noisy feedback, that is, certain discourse patterns that differ in frequency depending on the grammaticality of children’s utterances. However, no one has explicitly discussed how children could use noisy feedback, and I show that noisy feedback is unlikely to be necessary for language learning because (a) if noisy feedback exists it is too weak: a child would have to repeat a given sentence verbatim at least 8.5 times to decide with reasonable certainty that it is ungrammatical; (b) no kind of noisy feedback is provided to all children at all ages for all types of errors; and (c) noisy feedback may be an artifact of defining parental reply categories relative to the child’s utterance. For example, because nearly all parental speech is grammatical, exact repetitions (verbatim repetitions of child utterances) necessarily follow more of children’s grammatical utterances than their ungrammatical utterances. There is no evidence that noisy feedback is required for language learning, or even that noisy feedback exists. Thus

Correspondence too: Gary F. Marcus, Department of Brain and Cognitive Sciences, Massachusetts

Institute of Technology, Cambridge, MA 02139, USA; e-mail [email protected].

*Many of the ideas in this paper grew out of discussions with Steven Pinker: without him this paper

would not exist. I wish to thank both Steve Pinker and John Rosen for extremely helpful comments at

every stage of the preparation of this manuscript, two anonymous reviewers, S. Avrutin, P. Bloom, S.

Crain, K. Olguin, N. Pearlmutter, D. Poeppel, D. Slobin, E. Stein, and especially Fei Xu, for comments on drafts of this paper, J. Stern and T.J. Rosen for statistical help, and M. Bowerman, E. Clark, H. Clark, S. Prasada and V. Valian for helpful discussion. The author was supported by an

NDSE Graduate Fellowship and NIH Grant HD 18381 and NSF Grant BNS 91-09766 to Steven Pinker.

OOlO-0277/93/$05.00 @ 1993 - Elsevier Science Publishers B.V. All rights reserved.

54 G. F. Marcus

internal mechanisms are necessary to account for the unlearning of ungrammatical utterances.

Introduction

A major challenge for theories of language acquisition is to explain how children

recover from grammatical errors, such as (1) and (2):

(1) ‘1 maked it with water. (Sarah 4;5; Brown, 1973)

(2) *And fill the little sugars up in the bowl. (Mark 4;7; Pinker, 1989)

Do children eliminate their grammatical errors solely on the basis of internal

mechanisms, or do they require external feedback from their parents?

Brown and Hanlon (1970) carried out two analyses in the first systematic

examination of whether parents provide feedback contingent on children’s gram-

matical errors. In the first, they examined whether parents comprehend their

children better if their children’s utterances are grammatical. Each child question

was classified as grammatical or ungrammatical; each parental reply was coded to

indicate whether the parent understood or failed to understand the child’s

utterance. Replies indicating the lack of comprehension followed about as many

grammatical child questions (42%) as ungrammatical ones (47%); similarly,

replies indicating comprehension were equally likely following grammatical and

ungrammatical speech (45% in both cases). Brown and Hanlon concluded that

“In general, the results provide no support for the notion that there is a

communication pressure favoring mature constructions” (p. 45).

In their second analysis, Brown and Hanlon coded whether parental replies

indicated approval (e.g., That’s right or Yes) or disapproval (e.g., That’s wrong or

No). Again, there was no relation between parental reply types and child

grammaticality. Finding not “even a shred of evidence that approval and dis-

approval are contingent on syntactic correctness” (p. 47), Brown and Hanlon

concluded that:

While there are several bases for approval and disapproval, they are almost always semantic or

phonological. Explicit approval or disapproval of either syntax or morphology is extremely rare in

our records and so seems not to be the force propelling the child from immature to mature forms.

(P. 48)

Based largely on their conclusions, much subsequent research in language acquisi-

tion has tried to solve the puzzle of how children acquire language solely from

positive evidence (i.e., hearing sentences that belong to a language) and without

negative evidence (i.e., information about which sentences do not belong to that

language) (e.g., Baker, 1979; Baker & McCarthy, 1981; Berwick, 1985;

Negative evidence 55

Bowerman, 1983, 1987, 1988; Braine, 1971; Chomsky & Lasnik, 1977; Fodor &

Cram, 1987; Grimshaw, 1981; Gropen, Pinker, Hollander, & Goldberg, 1991;

Lasnik, 1981, 1989; Marcus et al., 1992; Matthews & Demopoulous, 1989;

Mazurkewich & White, 1984; Pinker 1984, 1989; Roeper, 1981; Wexler Br

Culicover, 1980; Wexler & Hamburger, 1973; Wexler & Manzini, 1987.)

The “no negative evidence problem” - that is. how children could learn

language without negative evidence - is often seen as necessarily tied to nativist

explanations that posit the existence of internal and innate mechanisms. In fact,

Braine (1971), the first to discuss the implications of the “no negative evidence”

problem, used the problem to argue against Chomsky’s (1965) nativist explana-

tion of language acquisition. Arguing that Chomsky’s hypothesis-testing proposal

would require negative evidence, Braine presented anecdotal evidence suggesting

that negative evidence was insufficiently frequent and perhaps ignored, hence

refuting Chomsky’s proposal.

Without negative evidence, any model of language acquisition, nativist or not,

must account for how the child can learn language from positive evidence alone.

Suppose a child must learn that a certain sentence, B, is ungrammatical. The child

might learn this in two ways. First, something external to the child (i.e., explicit

negative evidence) could tell the child that B is ungrammatical. If the parent does

not provide an explicit denial of sentence B, the only alternative is that the parent

says a sentence (or a set of sentences), A, and that the child has a mechanism

which eliminates B when given A. That mechanism, innate or learned, must be

internal to the child, regardless of whether it is, for example, a general pragmatic

mechanism or a linguistically specific mechanism. The existence or non-existence

of negative evidence allows us to determine whether internal mechanisms are

needed. If negative evidence does not exist, the task of language acquisition

researchers must be to discover which internal mechanisms do allow children to

eliminate their errors.’

Recently, in what I will call discourse studies, some researchers have disputed

the claim that there is no negative evidence (Bohannon & Stanowicz, 1988;

Demetras, Post, & Snow, 1986; Hirsh-Pasek, Treiman, & Schneiderman, 1984;

Morgan & Travis, 1989). These studies, reporting evidence from the distribution

of certain patterns of discourse between parents and children, argue that parents

“‘Indirect negative evidence” (e.g., Chomsky 1981) - information about which sentences have not

appeared in the input - is sometimes offered as a third type of evidence available to the child. The use

of indirect negative evidence would require an inference such as “If X appears in the input, assume

that Y is not in the language, unless you hear Y in the input.” Indirect negative evidence thus depends on a reanalysis of positive evidence based on mechanisms internal to the child, rather than input

external to the child; hence for the purposes of this paper I collapse it with positive evidence. See

Pinker (1989, pp. 14-15) for further discussion.

Marcus 56 G.F

Table 1. Definitions of types of parental replies used in discourse studies

Explicit approval

Non sequiturs

Repetitions (only Hirsh-Pasek et al.)

Imitations/exact reps.

Expansion

Recasts

Topic extensions

Move-onslno responses

Clarification questions

Confirmation questions

Parent says yes or uh-huh or the like

Parent fails to understand child

Parent repeats child utterance, perhaps with changes

Parent repeats child utterance,

verbatim

Parent repeats child utterance, but

makes grammatical changes or adds

new material

Parent repeats child utterances. but

with minor grammatical changes

Continued topic but not a repetition or

expansion

Parent moves conversation along

Parent asks a question that requests

child to repeat part of utterance

Parent asks a yes/no question

do provide implicit feedback to their children based on whether children speak

grammatically.’

Each study used somewhat different reply categories; the Appendix reprints

exact definitions. Table 1 provides rough definitions of each type of parental

reply. Some discourse patterns, such as expansions (interchanges between a child

and a parent in which a parent repeats the child’s utterance with small changes),

are claimed to be elicited more often by ungrammatical speech than by grammati-

cal speech. Other discourse patterns such as exact repetitions (interchanges in

which a parent exactly repeats a child utterance) are claimed to be elicited more

often by grammatical speech than by ungrammatical speech.

In all cases, the differences in parental replies to grammatical versus un-

grammatical sentences were statistical rather than categorical (i.e., all-or-none). I

call this type of feedback noisy feedback, since parents provided each type of

‘All of the studies that I will discuss contrast parental replies to grammatical sentences with

parental replies to ungrammatical sentences. However, one study, Moerk (1991), presented examples

only of how parents reply to ungrammatical sentences and failed to present examples of how parents

reply to grammarical utterances. For example, in the following exchange, Moerk called the reply What

did I do? a “correction” (Eve: What did you doed? Mother: What did I do?), but he neglected to note that the identical parental reply, two samples earlier, is not a “correction” (Eve: Wurt my eye.

Mother: Your eye? Eve: Yeah. Mother: What did I do?) (Eve, 2;l). Moerk provided no objective definition of “corrections” and no explanation of how a child could recognize or use them. Applying

this method, one could argue that the word red provides negative evidence: simply cull transcript

examples in which the parent said red following a child’s ungrammatical utterances and ignore the

occasions in which the parent said red after the child’s grammatical utterances. Without the crucial contrast between replies to grammatical and ungrammatical sentences, such studies are irrelevant to

the question of whether parents provide negative evidence.


reply after both grammatical and ungrammatical sentences, albeit in different

proportions.

In a recent discourse study, Bohannon and Stanowicz (1988) argue that

discourse-based noisy feedback “may be considered superior to simple denials

and as qualified to assume the role of ‘negative evidence’ ” (p. 688), and

concluded that “To the extent that current theories of language acquisition also

ignore adults’ tendency to provide feedback (i.e., negative and specific evidence),

these theories will fail to accurately account for language acquisition” (p. 688).

These conclusions, if correct, would undermine much of the research based on

the assumption that parents do not provide negative evidence. However, because

the methodology and results of the discourse studies vary and often conflict with

one another, and because there has been little discussion of how children could

use noisy feedback to eliminate grammatical errors, the role and existence of

noisy feedback remain controversial. This controversy is evident both empirically,

in the conflicting results and conclusions of Bohannon and Stanowicz (1988) and

Morgan and Travis (1989), and theoretically, in a recent debate between Gordon

(1990) and Bohannon, MacWhinney, and Snow (1990).

The goal of this paper is to define and apply clear criteria for clarifying the role

and existence of noisy feedback. These criteria will lead to the following

conclusions:

. Noisy feedback is too weak to be a plausible way of eliminating errors. Even

under statistically optimal conditions, a child would have to repeat a given

sentence verbatim more than 85 times to eliminate it from his or her grammar.

. Noisy feedback is inconsistent across parents, declines or disappears with age,

and is probably not provided for all types of errors and is thus unavailable for

much of language acquisition. Furthermore, some apparent patterns of noisy

feedback may be averaging artifacts that do not correspond to types of feedback

given to any individual child.

. Because parental reply categories are defined only with respect to the child’s

utterance, “correlations” between the two may be artifacts resulting from the

definition of parental reply categories and of constant noncontingent properties

of parental and child speech. For example, several studies show that verbatim

repetitions follow more grammatical than ungrammatical sentences. But be-

cause parents virtually never speak ungrammatically, verbatim repetitions

necessarily negatively correlate with children’s ungrammatical utterances.

Any one of these three conclusions, the weakness, the inconsistency, or the

inherently artifactual nature of noisy feedback, would by itself severely under-

mine, if not falsify, the position that parents provide feedback to their children

and thus that such feedback is required for language acquisition. Of course, even

if parents provided feedback, it might turn out empirically that children do not

use it. For example, Zwicky (1970), in discussing his daughter’s inflectional

58 G. F. Marcus

overregularizations (e.g., goed), points out that “six months of frequent correc-

tions by her parents had no noticeable effect”. Braine (1971) even more clearly

illustrates that feedback may be ineffective:

For experimental purposes, I have occasionally made an extensive effort to change the syntax of

my two children through correction. One case was use by my two-and-a-half-year-old daughter of

other one as a noun modifier. Over a period of a few weeks I repeatedly but fruitlessly tried to

persuade her to substitute other + N for orher one + N. With different nouns on different

occasions, the interchanges went somewhat as follows: “Want other one spoon, Daddy” - “You mean, you want THE OTHER SPOON” - “Yes, I want other one spoon, please, Daddy” - ‘Can

You say ‘the other spoon’?” - “Other one spoon” - “Say ‘other’ ” - “Other” -

“Spoon” - “Spoon” - “Other spoon” - “Other. spoon. Now give me other one spoon?” Further tuition is ruled out by her protest, vigorously supported by my wife. Examples indicating a

similar difficulty in using negative information will probably be available to any reader who has

tried to correct the grammar of a two- or three-year-old child. (pp. 160-161)

Even when children understand that they are being corrected, they sometimes

make incorrect generalizations, as McNeil1 (1966, p. 69) shows:

Child: Nobody don’t like me.

Mother: No. say “nobody likes me.”

Child: Nobody don’t like me.

[Eight repetitions of this dialogue follow.]

Mother: No, now listen carefully, say “NOBODY LIKES ME.”

Child: Oh! Nobody don’t likes me.

These examples suggest that it is the child’s underlying linguistic system, rather

than negative evidence, which forces children to change their grammars. Until the

existence of reliably parental feedback is firmly established, however, it is

premature to consider whether children actually use it.

Types of parental feedback and their role in language learnability

Positive evidence is simply the input, that is, the sentences children hear. In

contrast, negative evidence is a parental behavior that provides information about

when sentences are not in the language. Negative evidence does not tell a child

which sentences are grammatical; rather, it indicates that the child has uttered an

ungrammatical sentence. Moreover, negative evidence does not tell a child why a

particular sentence is ungrammatical.

A child who does not speak can receive no negative evidence, aside from

explicit metalinguistic statements (e.g., don’t say X). Negative evidence must

respond to a child’s utterance; it can only arise if parents are in some way sensitive

(though not necessarily consciously) to whether their children speak grammati-

tally The parental behavior that provides negative evidence I will call the reply type.

The reply type may take many forms: the parent might say 110, provide a


repetition, shrug, or even spank the child. An individual occurrence of a given

reply type (e.g., a single utterance of the word no) is a repfy instance. To distinguish three kinds of negative evidence that are often collapsed, I use

the terms complete feedback, partial feedback and noisy feedback. Complete feedback is any corrective signal provided for all and only those sentences that are

ungrammatical (cf. Gold’s (1967) term informant presentation in the formal

mathematical literature on learnability). Partial feedback is any corrective signal

provided following some ungrammatical sentences, but never provided following

correct sentences. Noisy feedback is a corrective signal provided after some errors

and after some correct sentences, but in different proportions. A single reply

instance of noisy feedback, unlike instances of complete feedback and partial

feedback, does not guarantee that a sentence is ungrammatical.

Verbal parental feedback, such as repetitions or expansions, inherently pro-

vides the child with positive evidence, as well as potentially providing negative

evidence. Several studies have reported that expansion may spur learning (though

Morgan, Bonamo, & Travis, 1991, conclude the opposite). Crucially, however,

even if children learn from expansions, they might do so without using negative

evidence. In principle, a child could learn whether some sentence is grammatical

(a) only from positive evidence, which tells the child that the parental utterance is

a possible way of saying what she wanted to say; (b) only from negative evidence,

which tells the child that her utterance is not acceptable; or (c) both, which would

tell the child both that her sentence was unacceptable and provide an acceptable

alternative; each of these possibilities is plausible a priori. Consider this hypo-

thetical dialogue:

(3) Child: I eated the food.

Parent: I ate the food.

This parental reply clearly provides the child with a piece of positive evidence: I

ate the food is a grammatical sentence. Positive evidence alone does not tell the

child whether eated and ate are stylistic variants or synonyms or whether eated is

unacceptable, but might do so in combination with internal mechanisms. The

parental reply could serve as negative evidence only if the child recognizes it as an

exemplar of a recast and has mechanisms that use such information.

Complete feedback

A child who received complete feedback might eventually converge on the correct

language by eliminating all possible but ungrammatical sentences from her

language (Gold, 1967; Pinker 1979).

If complete feedback existed it would probably be easy to detect, since there

would, by definition, be a perfect correlation between the reply type and the

60 G. F. Marcus

grammaticality of the child’s utterance. Nobody, though, has ever provided any

evidence that children receive complete feedback; every reply type studied in the

discourse studies is not provided for all ungrammatical sentences, and is provided

for some grammatical sentences. Nobody claims, for instance, that parents

expand children’s utterances every time that a child errs but never when the child

speaks grammatically. Thus children almost certainly do not receive complete

feedback.

Partial feedback

Partial feedback, by definition, is not provided every time a child makes an error.

There has been no explicit discussion of how children could use such feedback,

although Gordon (1990) has suggested that “it may, in fact, be possible to show

that learning can occur with inconsistent feedback . . . using statistical rather than

absolute criteria to determine grammaticality” (p. 219). It is not clear whether

children have mechanisms for using partial feedback, nor what those mechanisms

might be.

In any case, partial feedback does not seem to exist. No reply type studied in

the discourse studies is provided only for ungrammatical sentences but not for

grammatical sentences, or vice versa. The evidence from the discourse studies

suggests that all patterns of discourse provide, at best, noisy feedback: every reply

type is provided following both grammatical and ungrammatical speech.

Noisy feedback

Several studies claim to have documented patterns of noisy feedback, but there

has been no explicit discussion of how children might use it. I will examine a

concrete example, after defining four terms. The proportion of reply instances

(e.g. expansions) elicited by grammatical speech will be denoted by pr{gr}. The

proportion of reply instances elicited by ungrammatical speech is, then, pr{ungr}.

The number of times the child tests a given sentence is n; the observed proportion

of reply instances is p(obs). I will assume that the feedback is provided prob-

abilistically and independently.

Suppose pr{ungr} = .20 and pr{gr} = .12 (These proportions are drawn from

the distribution of noisy feedback reported by Hirsh-Pasek et al.) Suppose the

child says a sentence once (i.e., II = 1). Depending on whether the parent

provides a reply instance, p(obs) will be either 0 or 1. Suppose p(obs) is 1; given

the small sample size, p(obs) could easily come from either distribution. The


chance that p(obs) comes from pr{ungr} is .625 (since 20 out of every 32 reply

instances would follow ungrammatical sentences). The chance that it comes from

pr{gr} is ,375 (=l - .625). Thus if the child decides that the sentence is

ungrammatical, there is a .375 chance that the child is wrong. Or if p(obs) is 0,

there is a .52 (881168) chance that the sentence is grammatical, and a .48 chance

that the sentence is ungrammatical. In either case, the child has some information

but not enough.

The child’s chances improve if the child increases the sample size, n, by

repeating the sentence. Suppose after 100 repetitions of the sentence, p(obs) =

.17. Then it is relatively likely that the sentence is from pr{ungr} but still

reasonably likely that p(obs) comes from pr{gr}. If a child repeats the test

sentence 1000 times, with p(obs) = .20, the child could decide with near certainty.

In general, the more times the child repeats the same sentence, the more

information the child gathers, and the easier it is for the child to determine the

grammaticality of that sentence, with some degree of certainty; I will assume that

the degree of certainty equals the rate of error.

Because the end point of language acquisition is the adult state, I assume that

the acceptable rate of error, F, should reflect the rate at which adults make

grammatical errors (or perhaps be lower, since adults often know when they have

made errors). If E is too high, the child will fail to converge on the adult state of

rarely making errors. The overall rate of adult past tense overregularization errors

(e.g. maked or maded) is around .00004 (Marcus et al., 1992), while the overall

rate of adult speech errors is about .OOl (Stemberger, 1989). To be generous by

an order of magnitude, suppose E is .01.3

In Figure 1, the left curve represents the sampling distribution of the propor-

tion of parental reply instances out of child utterances provided following

grammatical sentences, while the right curve represents the sampling distribution

of the proportion of parental reply instances out of child utterances provided

following ungrammatical sentences. The shapes of the two curves depend on the

proportions of feedback to grammatical and ungrammatical sentences and the

number of times, n, that the child repeats the test sentence; here pr{gr} = .12,

pr{ungr} = .20, y1= 10.

In order to decide whether a sentence is grammatical, assuming E = .Ol, a child

must determine whether p(obs) is within the 99% confidence interval of the

grammatical distribution, within the 99% confidence interval of the ungrammati-

cal distribution, or within the overlap between the two confidence intervals, which

I call the region of ambiguity, shown as the cross-hatched region in Figure 1. This

‘Actually, two error rates are involved here: the chance of incorrectly accepting a sentence as grammatical and the chance of incorrectly accepting a sentence as ungrammatical. Since most speakers

agree both on which sentences are grammatical and on which sentences are ungrammatical, both rates should be very low. Lacking evidence to the contrary, I assume that these two error rates are equal.

62 G. F. Marcus

Figure 1.

PI+}= -12 Prbngr}=.20

OfI 0.1 02 03 OA 05 0.4 0.7 0.8 0.9 la

p(obs) Obsewed proportion of reply instances out of child utterances of a given sentence

Proportion of child utterances of a given sentence which are followed by a reply instance, given n = IO. The vertical line, at p(obs) = .36, represents the upper bound of the 99% confidence interval of pr{gr). The cross-hatched region of ambiguity represents the range of possible proportions of feedback which fall within the 99% confidence intervals of the distributions of parental responses both to grammatical and ungrammatical sentences. The dotted region to the right represents the area of confidence interval of pr{ungr} that is not within the confidence interval of pr{gr}.

region indicates possible values of p(obs) under which a child cannot make a

decision within the specified risk of error.4

The only way the child can reduce the region of ambiguity is to repeat her test

sentence again and again, n times. Figure 2 represents the smallest value of n in

which the region of ambiguity is eliminated (for F = .Ol). Before being able to

make a decision, the child would need to repeat the same construction 446 times.

Of course, the minimum number of repetitions necessary to decide whether a

sentence is grammatical depends on the proportions of feedback; these values

‘Note that for positive evidence there is virtually no region of ambiguity. If the parent says a

sentence, the child can be nearly certain that the sentence is grammatical. According to Newport.

Gleitman, and Gleitman (1977), 99.44% of parental speech to children is grammatical. Similarly, if the parent provided complete feedback, there would also be no region of ambiguity. Upon hearing a

reply instance, the child could immediately decide that a given sentence was ungrammatical.


PI-&r}=_12 Prhmgr}=.20

1

03 OR 05 Ob 0.7 08 0.9 lfl

pbbs)

Obsewed proportion of reply instances out of child utterances of a given sentence

Figure 2. Proportion of child utterances of a given sentence which are followed by a reply instance, given n = 446. The vertical line, at p(obs) = .16, represents both the lower bound of the 99% confidence interval of pr{ungr} and the upper bound of the 99% confidence interval of pr{gr}. Thus, the region of ambiguity is zero. The left region indicates the confidence interval of pr{gr}. The right, dotted region, represents the confidence interval of pr{ungr}.

vary across the discourse studies. Table 2 shows estimates of y1 for the clearest and

easiest reply types the child could use. Weaker differences between parental

replies to grammatical and ungrammatical sentences would require the child to

repeat a test sentence even more often.

The lowest estimate of II, derived from data reported by Bohannon and

Stanowicz (1988), is 85; the highest estimate of II is 679. If a child does not repeat

a given sentence n times, noisy feedback cannot account for how the child

eliminates the error.

However, aside from formulas and routines, most of children’s speech is not

repetitive. Children repeat few sentences even ten times, let alone 85. For

example, Pinker (1989) searched 86,332 child utterances taken from transcripts of

spontaneous speech for errors in which a child misused the argument structure of

a dative (e.g., Don’t say me that). None of these errors was repeated anywhere

near 85 times: one child (Eve) made 11 errors with the verb write, no other error

64 G.F.

Table 2. Minimum number of times (n) a child would need to repeat a given

sentence verbatim to decide whether it was grammatical, with chance of

error, E, less than .Ol, calculated for the strongest reply types reported in

the discourse studies (n may be determined by finding the minimum

number of repetitions of a single sentence such that the 99% confidence

intervals of the two distributions (pr{gr}, pr{ungr}) do not overlap)

Study

Hirsh-Pasek et al.

Penner

Bohannon and Stanowicz

Morgan and Travis

Reply type prfungrl pr{gr) n

Repetitions 2-year-olds 20 12 446

3-S-year-olds no differences n/a Expansions: 1 group 18.3 4.6 104

Expansions: group 2 11.3 6.3 679

Total of all reply types 35 14 85

Expansions (A. E. and S) 11.3 2.7 169

Note: The data from Demetras et al. are excluded because most patterns of reply varied

across parents and no inferential statistics (or sample sizes) were provided. Without such

information we cannot infer the reliability of the data. The data for Morgan and Travis

are an average across the patterns of parental expansions to Adam, Eve. and Sarah,

from Table 4. Morgan and Travis (1989, p, 545). because there is substantial variation

between the pattern of expansions to the different children. Eve would only require 63

verbatim repetitions, but Sarah would require 300.

was repeated more than three times, and thus noisy feedback is almost certainly

too weak to account for how children eliminate their errors.

Children might follow strategies other than the one I have outlined, but none

of these can reduce n without increasing the error rate. For instance, children

might be thoroughly productive and assume that every sentence is grammatical

unless the sentence receives frequent and repeated correction. Following this

strategy, children would overgenerate implausibly often, repeating ungrammatical

sentences far more often than they are actually observed to do (Marcus et al.,

1992). Children also cannot be completely conservative and assume that all

sentences are ungrammatical, since they productively create sentences they have

never heard (e.g., Pinker, 1989). In any case, if children utilize noisy feedback

before repeating a sentence enough times, their risk of errors must go up, because

there is only a limited amount of information in each reply instance, and the only

way to get more information is to repeat their sentences again and again in an

effort to increase the reliability of the information contained in parental replies.

Combining noisy feedback from different sentences

I have assumed that children determine grammaticality on a sentence-by-

sentence basis. Could children instead determine the grammaticality of entire

classes of sentences on the basis of negative evidence? For instance, a child trying

to test whether The boy eat apples is grammatical might combine feedback


provided to that sentence with feedback provided to “equivalent” sentences such

as The girl eat apples, in order to overcome the inherent weakness of noisy

feedback.

Combining feedback provided to some set of equivalent sentences requires a

child to determine which sentences are “equivalent”; determining equivalency,

however, can only be done properly after the child knows which factors affect a

sentence’s grammaticality, defeating the very purpose of using noisy feedback.

Sometimes two sentences similar in structure, differing by no more than a word,

are both equally acceptable in a language; for example, A boy ate some apples and A girl ate some apples are both grammatical, and Some a boy apples ate and

Some a girl apples ate are both ungrammatical. Often, however, two apparently

quite similar sentences are not equally acceptable in the target language. For

example, A boy ate some apples is grammatical but A boy ate much apples is

ungrammatical. A child who combined the feedback provided for these two

sentences would err, as would a child who combined feedback for *Fill the water in the bowl with Pour the water in the bowl, or John slapped Bill with *John hitted Bill. The rules governing which sentences are and are not equivalent, with respect

to feedback, are the very rules of the grammar the child is trying to learn. If

feedback is to be the means by which children form equivalence classes then

children’s use of feedback cannot rely on the pre-existence of those equivalence

classes. There is no doubt that children do form equivalence classes, but negative

evidence does not explain how children form them.5

Learning the probabilities of noisy feedback

The model presented above assumes that the child has perfect knowledge of

(pr{gr} and pr{ungr}). If the child’s knowledge of the reply probabilities is poor,

errors of falsely accepting ungrammatical sentences or else errors of falsely

rejecting grammatical sentences becomes more likely. For instance, if pr{gr} =

.12 and pr{ungr} = .2, but the child incorrectly hypothesizes that pr{gr} = .2 and

pr{ungr} = .4, and the child utters a grammatical sentence multiple times and

receives p(obs) = .2, the child will conclude falsely that the sentence is gram-

matical.

Given individual differences between parents (to be discussed below), it is

unlikely that the probabilities of feedback are specified innately. How, then,

could the child learn the reply probabilities? The child cannot simply record how

many of her ungrammatical versus grammatical sentences elicit instances of some

reply. Children could safely assume that their parents speak grammatically, but by

‘The child learning from positive evidence alone may seem to face the same dilemma- how to form the equivalence classes without knowing them. The answer proposed by Chomsky and others is

that the child has innate knowledge which constrains the inductions by which the child may form

equivalence classes.

hypothesis they do not know which sentences are ungrammatical. A child might

construct minimal pairs by comparing the parent’s sentence with a sentence that is

likely to be ungrammatical. But this begs the question: how would the child know

which sentences are likely to be ungrammatical? In sum, it is unclear how children

could learn the probabilities of feedback.

Some researchers seem to want to eliminate language-specific learning mecha-

nisms in favor of parental feedback on the grounds that models that depend on

parental feedback might be simpler, but consider what new mechanisms they must

propose. The child must recognize the (subtle) feedback reply types and discrimi-

nate the useful reply types from the noise, and then make use of them.

Furthermore, the child must learn (at least approximations of) the probabilities of

feedback, induced in some unspecified manner. Though a child might solve all

these problems, it is hardly clear that models of language acquisition that depend

on feedback present simpler models than those based on internal, linguistic-

specific constraints.

Summary

I distinguished three types of negative evidence: complete, partial, and noisy

feedback. There is no evidence that either complete feedback (negative evidence

provided following all ungrammatical sentences and no grammatical sentences) or

partial feedback (negative evidence provided for some ungrammatical sentences

but no grammatical sentences) exists. Noisy feedback, the only attested type of

feedback, is negative evidence provided for some grammatical sentences as well

as some ungrammatical sentences. Under conditions of noisy feedback (unlike

complete feedback and partial feedback), a single reply instance cannot guarantee

that a given sentence is ungrammatical. Under certain reasonable assumptions

about feedback probabilities and acceptable error levels, a child would have to

repeat the sentence in question, verbatim, at least 85 times before deciding

whether it is grammatical. Furthermore, to use noisy feedback, the child must

solve the difficult bootstrapping problem of determining the probabilities of reply

instances for both grammatical and ungrammatical sentences. Theories of lan-

guage acquisition that require noisy feedback are thus plausible only to the extent

that it is plausible that children notice noisy feedback, have mechanisms to make

use of it, and repeat sentences at least 85 times each.

Generality and availability of noisy feedback

Noisy feedback is interesting only if it can eliminate the need for specific internal

mechanisms, but these mechanisms are only eliminable if noisy feedback is


necessary for language learning. If noisy feedback were merely helpful for

language learning, but not necessary, internal mechanisms would still be needed

to account for language acquisition. In this section I will develop and apply

criteria, based in part on those discussed by Grimshaw and Pinker (1989), Pinker

(1989), and Morgan and Travis (1989), for determining whether there is evidence

that any type of feedback is a necessary component of language acquisition.

Criteria

Does every child receive noisy feedback?

Since every child learns language, a particular type of parental feedback can be

a precondition for learning language only if it is provided to every child. Many

types of feedback may be sufficient for language acquisition, but if any child

manages to learn language lacking that particular type of feedback, then that

particular type of parental feedback cannot be necessary for language acquisition.

(Note that every child receives positive evidence.)

Because between-subject differences are crucial, appropriate statistical analy-

ses of patterns of noisy feedback should examine patterns of feedback within

individual parent-child dyads. Combining data from several children may create

two types of averaging artifacts. First, aggregating data from multiple children

may hide differences between the patterns of feedback provided to those children.

Suppose one parent provided reliable noisy feedback, but another parent did not

provide reliable feedback. Combining the data from these two parent-child

dyads, one might falsely conclude that the pattern of feedback is available to both

children. To avoid such problems, a more fine-grained analysis is necessary.

Second, when studies average raw data6 from several dyads, patterns of noisy

feedback can emerge that no child actually received. For example, if 80% of

Johnny’s utterances are grammatical, and Johnny’s mother repeats a random 75%

of his utterances, but 60% of Billy’s utterances are grammatical and his mother

only repeats half of Billy’s sentences, at random, then combining the same

amount of data for both children will lead to the (false) conclusion that 64% of

grammatical utterances elicited repetitions, compared to only 58% of ungram-

matical utterances; see Table 3.

Do parents provide noisy feedback until errors stop?

If certain aspects of language acquisition depend on parental feedback, parents

must provide feedback until children have finished acquiring those aspects of

bAveraging percentages rather than raw data would prevent the emergence of entirely spurious

reply contingencies but could still conceal important individual differences.

68 G. F. Marcus

Table 3. How patterns of feedback could be an artifact of averaging data from several children

Johnny

Billy

Average

Grammatical

60180 = .75

30160 = .5

901140 = .64

Ungrammatical

15120 = .75

20/40 = .5

35160 = .58

Now: Number of utterances repeated out of 100.

language. Moreover, if feedback declines or disappears with age, combining data

might suggest falsely that noisy feedback is available, even if no child actually

receives such feedback. Suppose that a parent consistently repeats every utterance

of his or her child at age 2 but by the time the child is 3 the parent no longer

repeats many of the child’s utterances. If at age 2 the child produces 80%

ungrammatical utterances, but by age 3 the child only produces 60% ungrammati-

cal sentences, then, as shown in Table 4, one might conclude falsely that the

parent repeats a higher proportion of ungrammatical sentences than grammatical

sentences, even though no parent ever replies differentially to grammatical and ungrammatical sentences. The misleading conclusion results from (a) the parent’s

repeating fewer of the older child’s sentences and (b) the older child’s greater

proportion of grammatical sentences. Averaging data across different children of

different ages may cause similar artifacts.

Do parents provide noisy feedback for all kinds of linguistic errors?

Language has several components or levels of representation, including

phonological, syntactic, and semantic representations. There is empirical evidence

that parents reply to different types of errors in different ways. For example,

Brown and Hanlon (1970, p. 48) concluded that the “bases for approval and

disapproval. . are almost always semantic or phonological”. To show that

negative feedback is necessary for the elimination of errors of some kind,

phonological, morphological, syntactic, or semantic, one must provide evidence

that adequate feedback corresponding to that specific kind of error exists.

Table 4. How patterns of feedback could be an artifact of averaging over age

Grammatical Ungrammatical

2-year-old 20/20 = 1 80180 = 1

3-year-old 0140 = 0 0160 = .O

Average 20160 = .33 801140 = .53

Note: Number of utterances repeated out of 100.


Do parents provide noisy feedback for different types of grammatical constructions?

Parents might provide feedback for some syntactic constructions, but still fail

to provide feedback for other syntactic constructions. A child who received

parental feedback for, say, agreement errors (e.g., He eat the candy), but not for

improper locative verb alternations (e.g., Fill the little sugars up in the bowl), could not learn which locative alternations are permissible on the basis of parental

feedback. Parental feedback must be available for all grammatical constructions

for which it is posited to correct.

Summary

To determine whether a particular type of noisy feedback could be necessary for

unlearning errors, there are four criteria: (1) the reply type must be available to

all children; (2) the reply type must be available throughout acquisition; (3) the

reply type must be available for errors in each component of language; (4) the

reply type must be available after all types of errors within a given component.

Any pattern of noisy feedback that is necessary for language acquisition would

meet all of these criteria. Positive feedback meets all of them: all children, at all

ages, receive positive evidence for all types of representation and nearly all types

of constructions. Complete feedback, if it existed, would also meet these criteria.

Application of criteria

Does every child receive noisy feedback?

Many patterns of feedback were inconsistent across dyads within the studies

that reported them, as indicated by asterisks in Table 5. Futhermore, many of the

remaining effects failed to replicate in other studies.’ The rightmost column

indicates that only one pattern of feedback was provided to all children studied:

recasts. Bohannon and Stanowicz found that, on average, parents provided more

recasts after ungrammatical than grammatical sentences. However, though they

indicate that parents and non-parents replied differently, it is unclear whether

every child received more recasts after ungrammatical sentences; even recasts

may not be consistent across the children they studied.

The studies that allow examination of individual differences show that different

parents provide different, even conflicting, patterns of feedback. Demetras et al.

‘An anonymous reviewer suggested that differences in social or economic status might account for some of the variation in feedback.

70 G. F. Marcus

Table 5. Availability of particular types of feedback across all children studied

Did all children

receive the same

type of Found by Not found by feedback’?

Explicit approval BH. HPTS, P No Non sequiturs BH No

Repetitions HPTS DPS* No

Imitations (or exact repetitions) DPS, BS P, MT* No

Expansion P, BS DPS*, MT No

Recasts BS Yes

Topic extensions/move-ons DPS P,* MT* No Clarification questions DPS, BS MT No

Confirmation questions P, MT No

Notes: Morgan and Travis distinguished partial and exact imitations. Exact imitations

were consistent across parents; partial imitations were not.

Penner found that confirmation questions were more common after ungrammatical

sentences; these effects, however, were not statistically significant.

*Indicates that the effect found was inconsistent across children within that study.

BH, Brown and Hanlon; HPTS, Hirsh-Pasek et al.; DPS, Demetras et al.; P, Penner;

BS, Bohannon and Stanowicz; MT, Morgan and Travis.

found that some children receive certain reply types, such as expanded repeti-

tions, more after ill-formed sentences than well-formed sentences.’ However,

other children receive the same reply types more often after well-formed sen-

tences. Penner noted that “although parents repeated correct child utterances

slightly more frequently than incorrect child utterances, the pattern was not

consistent for all parents”. Morgan and Travis, studying three subjects, Adam,

Eve, and Sarah (from Brown, 1973), found that, for each set of parents, the

contingencies between parental replies and the grammaticality of children’s

utterances were different. For example, while Adam’s parents asked more

clarification questions after his well-formed wh- questions, Eve and Sarah’s

parents were more likely to ask clarification questions after their children’s

ill-formed wh- questions. If the reply types are contingent on grammaticality for

some children, but contingent on ungrammaticality for other children, would

some children eliminate goed in favor of went, while other children eliminate went

in favor of goed?

Finally, Hirsh-Pasek et al., Penner, and Bohannon and Stanowicz all combined

data from many children in their analyses,” leading to potential statistical artifacts.

Data from children who received no feedback, when averaged with data from

‘Demetras et al. presented no inferential statistics, and many patterns of feedback are different for different parent-child dyads. Thus contingencies within individual dyads may be due to chance or

sampling error. “Penner provided information about the reliability of patterns of feedback across parents, but the

other two studies do not.


children who did receive feedback, might incorrectly suggest that feedback is

available to all children. Moreover, as shown above in Table 4, it is even possible

that some alleged patterns of feedback were not provided to any children.

In fact, there may be no type of feedback that is provided universally. Gordon

(1990) argued that in the Piedmont Carolinas, and possibly in other cultures,

parents rarely speak directly to their children. The existence of cultures in which

parents do not provide any feedback would prove that children can learn from

positive evidence alone and that no form of feedback can be a necessary

precondition to learning language.

Bohannon et al. (1990, p. 224) criticize Gordon’s example as being “an

anecdote . . . [that] hardly constitutes believable counterevidence”. In fact, Gor-

don’s example is based on a well-documented ethnographic study from Heath

(1983), from which I quote:

Trackton adults do not see babies or young children as suitable partners for regular

conversation [Ulnless they wish to issue a warning, give a command, provide a recommenda-

tion. or engage the child in a teasing exchange, adults rarely address speech specifically to very

young children. (p. X6)

Many other cultures with markedly different patterns of parent-child interaction

exist. Ochs and Schieffelin (1984) discuss two such cultures. (See also Eisenberg,

1982; Pye, 1986.) In Kaluli, extensive adult modeling is reported, along with a

lack of expansions - apparently without any evident consequences for either rate

or success of acquisition:

In addition to instructing their children by telling them what to say in often extensive interactional

sequences, Kaluli mothers pay attention to the form of their children’s utterances. Kaluli correct

the phonological, morphological, or lexical form of an utterance, or its pragmatic or semantic

meaning. (p. 293)

Rather than offering possible interpretations or guessing at the meaning of what a child is saying, caregivers make extensive use of clarification requests such as “huh?” and “what?” in an attempt

to elicit clearer expression from the child. However, caregivers do not elaborate or expand

utterances initiated by the child. (p. 294)

In the case of Samoan, parental feedback is minimal - again, with no apparent

consequences for acquisition:

[Claregiver speech is largely talk directed a/ the infant and typically caregivers do not engage in

“conversations” wirh infants over several exchanges. When a small child begins to speak, he or

she learns to make his or her needs known to the higher ranking caregiver. The child learns not to

necessarily expect a direct response. (p. 296)

Procedures for clarification are sensitive to the relative rank of conversational participants in the

following manner. If a low status person’s speech is unclear, the burden of clarifications tends to

be placed more on the speaker. [This] situation applies to most situations in which young children produce ambiguous or unclear utterances. Both adult and child caregivers tend not to try to

determine the message content of such utterances by, for example, repeating or expanding such an utterance with a query intonation, A caregiver may choose to initiate clarification by asking

72 G. F. Marcus

“What?” or “Huh?” but it is up to the child to make his or her speech intelligible to thk addressee.

(P. 298)

Even if Bohannon et al. concede such examples, they still argue that

The absence of a particular form of feedback in a particular community does not belie its utility for

those children who do receive it, nor does it mean that no form of feedback is necessary for

language learning to proceed normally. (1990, p. 224)

Although it is true that some form of feedback may be sufficient for those who

receive it, any type of feedback that is not available universally cannot be a

necessary type of feedback. (This does not eliminate the possibility that some

other form might be necessary.)

Could different children use different reply types to learn language? In that

case, each child would need to determine which types of feedback his or her

parents provide. One might argue that children attend to all possible reply types,

and that the reply types that their parents do not use in a manner contingent on

grammaticality have no net effect on the child’s grammar. But if, for example,

some parents use repetitions to indicate grammaticality whereas other parents use

repetitions to indicate ungrammaticality, then each child would have to determine

whether his or her parents’ repetitions correlate positively, negatively, or not all

with grammaticality.

Determining the status of possible reply types raises three problems. First, the

child can only calculate a given reply type’s status if the child knows which

sentences are grammatical. But this is precisely the knowledge the child is trying

to acquire. Second, the bootstrapping problem - determining the probabilities for

a particular reply instance without knowing which sentences are ungrammatical -

is worse if the child does not know which reply types are and are not contingent

on grammaticality. As the child tests more reply types for possible sources of

feedback, the child’s chance of falsely concluding that some reply type is

contingent on grammaticality increases (just as running many t tests increases the

chance of a type I error). Finally, learning which reply types are useful may

require the child to have an unrealistically large memory and unrealistically

powerful processing capacities, because the child would have to record whether

each possible reply instance occurred for every sentence or at least for enough

sentences to discover reliably the reply instance probabilities of a given type of

feedback for a grammatical versus an ungrammatical sentence.

In sum, the only plausible way that some pattern of noisy feedback could be

necessary for language acquisition is if every parent provides the same reply type

to every child, and the child is predisposed to expect that reply type to be

contingent on grammaticality. But the empirical evidence, both within the

discourse studies and across cultures, strongly suggests that no single pattern of

feedback is available to all children, and hence noisy feedback is unlikely to be

necessary for language acquisition.

Negalive evidence 73

Do parents provide noisy feedback until errors stop?

Although several studies appear to show that noisy feedback is available to

2-year-olds, they also show that noisy feedback diminishes rapidly or even

disappears altogether. Hirsh-Pasek et al. found that noisy feedback disappears with age: “. . . . sensitivity to well-formedness is only apparent among [parents of]

2-year-olds. The same pattern of results failed to emerge at other ages” (p. 86).

Penner studied two groups of children, and the older group (mean age = 3;O) received weaker feedback on all measures that the younger group (mean age =

2;O). Morgan and Travis found that parental feedback provided to Eve declined

significantly from the start of data collection (1;lO) to the end of data collection

(2;3). Neither Adam nor Sarah showed significant parental reply contingencies

after age 4. In sum, there is no evidence that children over 4 receive any noisy

feedback.“’

Yet children continue to learn language after feedback has disappeared. Many

types of linguistic errors persist throughout the preschool years. Sarah said I

maked it with water at age 4;5 (Brown, 1973). She makes these inflectional errors

at a greater rate at age 5 than at age 2;6 (Marcus et al., 1992). These errors

continue into at least first grade and perhaps as late as 9 or 10. Similarly, locative

errors, such as Mark’s And fill the little sugars up in the bowl (from Pinker, 1989)

occur until at least age 7 (Bowerman, 1988). Thus noisy feedback, given its

decline over time, is extremely unlikely to account for the unlearning of many of

these errors.

Do parents provide noisy feedback for all kinds of linguistic errors?

Hirsh-Pasek et al., Demetras et al., and Penner collapsed errors of many

linguistic components (e.g., syntax, phonology, and semantics), making it imposs-

ible to distinguish whether parents provide feedback for all types of errors or only

for some types of errors. Hirsh-Pasek et al. and Demetras et al. both collapsed

errors of phonology (e.g., evelator instead of elevator) with syntactic errors in

which words were misplaced or left out entirely. Penner combined morphological

errors (e.g., I ringed the bell) with syntactic errors (e.g., I rang bell), and perhaps

phonological errors as well.” Bohannon and Stanowicz distinguished phonological

errors from syntactic errors but collapsed morphological and syntactic errors.

These studies thus shed little light on whether noisy feedback is provided for

different types of errors (c.f. Valian, in press).

‘“Furthermore, Bohannon and Stanowicz averaged data from different children of different ages

and thus some alleged patterns of feedback might be the result of averaging artifacts. “It is unclear from Penner’s text how phonological errors were treated, but Bohannon and

Stanowicz (1988) write that “Penner (1987) lumped pragmatic, semantic, syntactic, and phonological

errors into a single category of ill-formed children’s speech” (pp. 684-685).

14 G. F. Marcus

The very limited data available suggest that it is unlikely that parents provide

adequate feedback for many types of errors. Bohannon and Stanowicz found that

parents are much more likely to correct semantic errors than syntactic errors

(88.6% vs. 35.9%). Morgan and Travis, the only researchers to separate particu-

lar types of grammatical errors, found that none of the children they studied

received any statistically valid reply types contingent on the grammaticality of

specific types of linguistic errors, after age 4. In sum, there is little evidence that

parents provide feedback for anything other than the truth value and phonology

of their children’s utterances, consistent with the conclusions of Brown and

Hanlon (1970).

Do parents provide noisy feedback for different types of grammatical constructions?

Only Morgan and Travis (1989) present data that allow construction-wise

comparisons. These data suggest that different types of linguistic errors may

receive opposite types of feedback. For example, since overall Adam’s parents

asked more clarification questions following ill-formed utterances (e.g., past tense

errors) than well-formed utterances, Adam might infer that clarification questions

indicate grammatical errors. But Adam’s parents asked more clarification ques-

tions after well-formed wh- questions (questions containing who, what, where, when, which or why). If Adam eliminated those sentences to which his parents

replied with clarification questions, he could reduce his past tense errors only to

the detriment of his use of wh- questions, or vice versa. To use the parental

feedback in clarification questions, Adam would need to learn different response

contingencies for different grammatical forms; it is far from clear how Adam

could figure this out. Finally, suppose Adam asked a wh- question with a past

tense form (e.g., Who runned?) and his mother replied with a clarification

question. How would Adam determine whether his mother was correcting his wh-

question syntax or correcting his past tense formation?

Summary

There is no evidence that any type of parental feedback is available widely

enough to obviate the need for specific linguistic mechanisms. Only one type of

noisy feedback (recasts, examined in only one study) was available to all the

children studied. No other pattern is provided consistently. No study showed

patterns of complete, partial, or even noisy feedback available for children over

age 4 despite the fact that children continue to make errors after this age. Every

study except Morgan and Travis (1989) collapses morphological and syntactic

errors; several studies even collapse phonological errors with syntactic errors.


Furthermore, because of dubious practices of averaging data from different

children and from children of different ages, some patterns of feedback may

conceal individual differences showing that certain patterns of feedback were not

available to some children and hence not necessary for language acquisition.

Worse, some alleged types of noisy feedback may be completely artifactual and

never provided to any individual child. The existing evidence for noisy feedback

thus fails to withstand the weight of careful empirical scrutiny and provides no

evidence that noisy feedback is necessary for language acquisition.

Definitional artifacts

Many discourse studies classified parental replies in a manner confounded with

the grammaticality of children’s utterances, hence rendering the correlations

between parental replies and children’s grammaticality possibly artifactual. The

coding criteria for parental replies cause two serious problems. First, many types

of parental replies cannot be classified until one looks at the preceding child

utterance, and these replies are sometimes coded differently depending on the

grammaticality of a child’s utterance (Morgan & Travis, 1989; Valian, in press).

For example, some parental utterances might be coded as repetitions following

a grammatical child utterance, but as expansions following an ungrammatical

child utterance. The child says the identical utterance in (5) and (6), but the

utterance is deemed an expansion or recast in the former, and as a repetition in

the latter:

(5) Expansion or recast C: The ball falled down.

P: The ball fell down.

(6) Repetition C: The ball fell down.

P: The ball fell down.

Second, because parents nearly always speak grammatically (99.44% of their

utterances according to Newport, Gleitman, & Gleitman, 1977), certain parental

reply categories, such as repetitions, are biased to occur more often after

grammatical child utterances, while other types of parental coding categories,

such as expansions, are biased to occur more often after ungrammatical child

utterances. Thus some of the contingencies reported in the discourse studies

reflect the consequences of coding categories virtually defined in terms of the

grammaticality of the child’s utterances, rather than being the result of actual

parental sensitivity to the grammaticality of the child’s utterances (Valian, in

press, makes a similar point).

Consider the following analogy. Suppose that I claim that I can control the

76 G. F. Marcus

color of the sky by my choice of which shirt to wear on a given morning. Every

morning, an impartial observer records whether I wear a green shirt or a blue

shirt, and records sky color relative to my shirt color.

After gathering data, we find an interaction between sky color and shirt color:

if 1 wear a blue shirt then the sky may be the same color, but if I wear a green

shirt then the sky is never the same color as my shirt. One might then conclude

that the sky responds to, or is sensitive to, my choice in shirt color. But this

conclusion is false: the sky is not sensitive to whether I wear a blue shirt or a

green shirt.

The problem lies in the coding criteria for the sky’s “replies”. We code sky

color only with respect to shirt color. A blue sky is coded as “same color” if I

wear blue, but the same blue sky is coded as “different color” when I wear green.

The sky is not sensitive to my shirt’s color; the coding categories are. If we instead

simply record the absolute color of the sky, there would be no artifactual

contingency and we would not be misled: the sky is never green no matter what

shirt I wear, and the sky is equally likely to blue no matter what shirt I wear.

Exact repetitions

Repetitions, like sky color, are classified relationally. There is no sentence that is

a repetition independent of a child’s utterance. And just as the “contingency”

between relative sky color and shirt color is confounded with the fact that the sky

is never green, the “contingency” between exact repetitions and child gram-

maticality (i.e., exact repetitions follow more grammatical than ungrammatical

sentences) is also confounded. The contingency between repetitions and well-

formed child speech is inevitable given that parents speak grammatically. When

children speak ungrammatically, there is virtually no chance that their parents will

repeat their utterances verbatim. Conversely, when children speak grammatically,

their parents may repeat their utterance exactly. Demetras et al.‘s exact repeti-

tions, Penner’s repetitions, and Bohannon and Stanowicz’s exact repetitions are

all tainted in this way.” (See also Valian, in press.)

Similar problems beset the other parental reply categories that showed some

(albeit limited) contingency with grammaticality of children’s speech. Recasts,

expansions and clarification questions also can only be coded in relation to

children’s utterances and hence are inherently confounded with children’s gram-

maticality. For instance, the parental reply The ball fell down is coded as a recast

if the child speaks ungrammatically (e.g., The ball falled down) but as a repetition

rather than a recast if the child speaks grammatically (e.g., The ball fell down).

“Hirsh-Pasek et al.‘s category of repetitions differs from exact repetitions because they include

parental responses which contain small changes.


Thus a contingency between recasts and ungrammatical child speech does not

demonstrate that parents are sensitive to their children’s grammar. Whenever

some aspect of a child’s sentence is relevant to the definition of the adult’s reply,

and that aspect is correlated with grammaticality, any correlation between the

grammaticality of the child’s utterance and the type of adult reply will be

confounded.

Possible objections

Even if the observed patterns of feedback are the result of spurious correlations,

the child could still make use of the parental replies. However, parental replies

such as recasts and expansions appear not to reflect any parental sensitivity to

grammaticality. Parents who are insensitive to children’s grammaticality cannot

give children negative evidence (except through explicit metalinguistic statements

of the form Don’t say X); they can only give children positive evidence. Recasts

and expansions may serve as ideal positive evidence, but they do not tell children

what is not in the language.

Another possibility is that whenever a parent says something differently from

the child, the child should assume he or she has made an error. A child following

such a strategy would surely err: most parental utterances are different from their

children’s utterance even when the child speaks grammatically. For instance, a

child might say I want a cookie and the mother might naturally reply No, you’ve

already had three cookies. Discourse is driven by conversation, not implicit

language lessons. Parents may choose a different word or construction to empha-

size something different, or even change the topic entirely. Children who changed

their grammars every time the parent said something different would radically

damage their languages.

Summary

Coding parental replies relative to the child’s previous utterance, as has been

done often in the discourse studies reviewed here, leads to the possibility that the

resulting correlations do not reflect true parental sensitivity but instead reflect

only constant, non-contingent frequencies of certain kinds of child and parental

behavior.

The only evidence for noisy feedback comes from reply categories that are

definitionally flawed. There are some reply types that are not defined relationally,

such as explicit correction, and failures of comprehension (Brown & Hanlon,

1970). But everybody agrees that these reply types are not contingent on

grammaticality.

78 G. F. Marcus

Discussion

There are three serious problems with the position that parents provide negative

evidence to help their children learn language. First, if such feedback does exist,

it is too noisy to be used in practice. Second, it is not available to all children, not

available at all the relevant ages, and probably not available for many types of

errors. Third, reply categories have often been defined relative to the child’s

preceding utterance, and thus observed correlations between parental replies and

children’s utterances may simply be artifacts of the coding scheme. Any one of

these problems is enough to significantly undermine the position that parents

provide negative evidence to their children is significantly undermined.

Positive evidence, in contrast, suffers from none of these problems; nor would

complete feedback if it existed. If a parent says something once, the child can

assume that it is grammatical; the child need not wait for 85 repetitions. Positive

evidence is available to every child regardless of age for all types of representa-

tion. Further, every parental utterance is positive evidence regardless of the child

utterance. If complete feedback (i.e., negative evidence in the sense used by

learnability theorists) existed, it would also meet every test I have applied. If

parents provided some reply type following all and only ungrammatical sentences,

then a single utterance would be a guaranteed test for ungrammaticality, not the

85 times necessary for noisy feedback. Complete feedback would be available by

definition to all children at all ages for all types of errors and could be coded

independently of children’s utterances. But complete feedback apparently does

not exist - nobody has ever claimed that parents correct all and only grammatical

errors.

The fact that there is independent evidence for internal mechanisms provides a

further argument against negative evidence. Consider errors such as Sarah’s Z

maked it with water. As children acquire the English past tense system, they

sometimes apply the regular past rule (add -ed) to irregular stems (e.g., go, make, or sing), thus producing erroneous past tense forms such as goed or maked (see Marcus et al., 1992). If negative evidence is not available, children must stop

producing these forms through some internal (possibly linguistically specific)

mechanism. Marcus et al. (1992) argue that children follow a principle of

inflectional blocking that prevents the application of a regular rule (add -ed to

form the past tense) whenever a child can retrieve an irregular past tense form for

some stem. For example, if a child attempting to mark the past tense of make retrieves made, the regular rule is blocked. If the child fails to retrieve an

irregular past tense form, the rule applies, and the child creates an incorrect form,

such as muked. As children’s retrieval of the correct past tense forms improves

through positive evidence, overregularization errors disappear.

Internal mechanisms, without the aid of negative evidence, could also elimi-

nate errors such as Mark’s Zfilled the sugars up into the bowl, or a similar error, Z


filled the water into the bowl. In these “locative” errors, children use verbs in

inappropriate syntactic constructions. The child has used the “content” argument

(the water) rather than the container “argument” (the bowl) as the object of the

verb fi11.13 In contrast, it is perfectly acceptable to use pour with its “content”

arguments as the object of the verb, as in I poured the water into the glass.

Negative evidence might drive locative errors out of a child’s grammar, but

without negative evidence children would need to eliminate errors through

internal mechanisms. Gropen et al. (1991) argued that locative errors result when

a universal linking rule, object affectedness, is combined with an improper

semantic representation of the verb Jill. The object affectedness rule states that the

direct object of a verb corresponds to an object that is specified as affected in

some particular way in the semantic representation of a verb. Gropen et al.

argued that in the adult grammar, the semantic representation of the verb fill does

not specify how the content is affected (a glass can be filled by pouring but also by

dipping or bailing), hence the content argument cannot appear as the object. In

contrast, the semantics of pour does specify that its content argument is affected

in a specific way, namely it must move downward in a stream, and hence it may

appear as the direct object of the verb. According to this theory, children always

follow the universal linking rule, but if they have an improper semantic repre-

sentation for a verb such as fiZ1, which does specify the manner of motion of the

content argument (e.g., being poured), then they would allow water to be the

object. Gropen et al. predicted that children who thought that fWs semantics

specified that its content argument was affected (e.g., by selecting pictures of

pouring as exemplifying fill) would be the same children who made syntactic

errors such as saying Fill the water into the sink. On their account, children could

learn the correct semantics using only positive evidence (e.g., hearing jZZ used

without pouring as when a cup is dipped in a punch bowl) and crucially, once the

semantics is learned from positive evidence, the linking rule fixes the syntax

automatically, allowing children to unlearn their errors without negative evidence.

If negative evidence really were generally available, it is unlikely that the

empirical evidence would support the existence of these mechanisms, because

they would be solutions to non-problems. But there is evidence for internal

mechanisms. For example, Marcus et al. (1992) showed that children are more

likely to overregularize verbs to which they have less exposure. As exposure to

correct past tense forms increases, overregularization errors decrease, hence

supporting the inflectional blocking hypothesis. Gropen et al. (1991) found that

semantic errors do indeed correlate with syntactic errors; children that make

semantic errors with fill are the same ones that use the wrong syntactic frames for

jifZ, hence supporting the existence of the object affectedness linking rule. These

“The precise details of the syntax and semantics and their relationship are outside of the scope of

this paper.

80 G. F. Marcus

examples suggest that internal linguistic mechanisms are real and that there is no

need for negative evidence.

Finally, it is important to reject the notion that nativist explanations of

language acquisition depend on the lack of negative evidence. Even if perfect

negative evidence were available, innate constraints on the generalizations which

children make would be necessary because many plausible errors simply never

occur. For instance, children never go through a period where they erroneously

form yes-no questions by moving the first is to the front of the sentence.

Although one can turn The man is hungry into Is the man hungry?, children

never, by a false analogy, turn The man who is hungry is ordering dinner into Is the man who hungry is ordering dinner? (e.g., Chomsky, 1965, 1980; Crain &

Nakayama, 1987). More generally, at every stage of language acquisition -

inferring the meaning of a new word or morpheme, creating a morphological or

syntactic rule, or determining the subcategorization frame of a new verb-the

child can make an infinity of logically possible generalizations, regardless of

whether negative evidence exists. The child simply cannot cycle through all logical

possibilities and check to see what his parents say about each one.

Children do learn languages; but they appear to do so without requiring

negative evidence: complete feedback and partial feedback do not exist. Noisy

feedback, the signal that has been claimed to exist, may largely be an averaging

artifact and is at best available in a fraction of the circumstances in which it would

be needed. Many of the observed patterns of noisy feedback are likely to be

averaging artifacts and definitional artifacts, but even if there were no artifacts,

the child would need to say a sentence such as Fill the little sugars up in the bowl more than 85 times to be sufficiently confident that it was an ungrammatical

sentence. There is no existing evidence that noisy feedback can account for the

unlearning of grammatical errors, and given the inherent weakness of noisy

feedback it is also extremely unlikely that any yet-to-be-discovered interactional

patterns would be adequate to account for language acquisition. These considera-

tions suggest that the problem of accounting for children’s avoidance and recovery

from errors in language acquisition is likely to be explained by the nature of their

internal learning mechanisms. The specific mechanisms I have discussed, such as

inflectional blocking and linking rules, are not the only ones that have been

proposed and may not be empirically correct. But any explanation of language

acquisition that depends on parental feedback seems unlikely to succeed, and

quantitative examinations of interaction patterns in parent-child conversation are

unlikely to shed much light on this important issue.

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Appendix: Definitions of parental reply categories

Hirsh- Pasek, Treiman, and Schneiderman (1984)

Strict repetitions: [were coded if the parent repeated] the child’s exact wording

with the possible exceptions that (a) ill-formed aspects were rendered in their

correct grammatical form as in People lives in Florida- People live in Florida. (b) I and you were appropriately interchanged.

Loose repetitions: [were coded if] (d) content words were replaced with proforms

or vice versa . . (e) modifiers were added or deleted . . . (f) a phrase of the

child’s utterance was repeated without the rest of the utterance . . or (g) the

child’s utterance was embedded with a longer utterance.


Demetras, Post, and Snow (1986)

Approvallcorrection: These utterances are explicit responses to the child’s preced-

ing utterance that either approve or give negative feedback to the child. Words

such as yes, no, that’s right, signal explicit feedback.

Repetitions: Four types of repetitions [were] coded: exact, contracted, expanded,

and extended. The use of deictic forms (e.g., substitution of you for me, come for go) are accepted as repetitions.

Exact repetitions: [were coded if the parental reply was] Exact repetition of what

the child said.

Contracted: [were coded if the parental reply was a] Shortening of the child’s

utterance in any way.

Expanded repetitions: [represented a] Correction of child’s utterance with appropriate syntax or morphology. Child: daddy house/Mother: Daddy’s house.

Clarification questions: These responses refer directly to the child’s preceding

utterance. Questions that start a new topic are not included. Also any

questions requesting knowledge from the child are not included. The different

types of questions are as follows:

Wh- [questions]: . . . must start with a wh- word and clarify, otherwise scored as a

Move-On.

Occasional questions: Questions that have a wh- word embedded in them: You

went where?

Repetition questions: These are repetitions (as described above) that have a rising

intonation contour at the end of the sentence.

Move-ons (MO): In these utterances the mother uses the same topic or starts a

new topic, but does not ‘negotiate’ with the child for meaning. We infer that

the mother understands what the child said, accepts it, and moves on with the

conversation.

Penner (1987)

Topic extensions: . . . continued the current topic of the interaction, but did not

qualify for the placement in another category, such as repetitions or expan-

sions. The topic was defined by the nonverbal as well as the verbal context of

the interaction.

84 G. F. Marcus

Verbal agreementiapproval: Included confirmations, agreements, or praise using

words like “Yes”, “That’s right”, “Good” and “OK”.

Expansions: Parents repeated all or part of the utterance and made additions and

other grammatical or semantic changes to words and morphemes in the

utterance. Parental responses that qualified as expansions were judged to

function to expand upon the previous child’s utterance (e.g., C: “Ball fall” A:

“The ball fell down”).

Repetitions: The parent repeated all or part of the child’s utterance without

adding to the utterance.

No response: The child’s utterance was followed by a pause of at least 2 sec. that

did not contain a verbal or nonverbal parental response or another child’s

utterance.

Confirming questions: included expansions and repetitions that were accompanied

by question intonation. Therefore, this category contained a subset of the

responses that were also defined as either expansions or repetitions.

Bohannon and Stanowicz (1988)

Exact Repetitions: Consisted of verbatim reproductions of the child’s entire

preceding utterance.

Contracted Repetitions: Consisted of the reproduction of a reduced set of ele-

ments from the child’s preceding utterance.

Expanded repetitions were coded if the adult reproduced major elements of the

child’s utterance and added new information.

Recasts [were coded] if the adult preserved the child’s meaning but replaced

elements of the child’s utterance (e.g., C: “That be monkey”; A: “That is a

monkey”).

Clarification questions were . . questions that related to the children’s previous

utterance without requesting any new information and counted other adult

repetitions with rising terminal intonation as exact, contracted, recasted, and

expanded.


Morgan and Travis (1989)

No Response: . . . if one or more child utterances immediately followed the

utterance containing the error and if no utterance in the subsequent adult

conversational turn was explicitly related (via complete or partial imitation) to

the error-containing utterance.

Expansions: If any utterance in the adult conversational turn following the

error. . . expanded the child utterance (e.g., C: Where other stick? P: Where is

the stick?).

Imitations: If the adult exactly repeated the erroneous utterance (reversals in

pronouns and deictic terms notwithstanding).

Clarification questions: If any adult utterance had the force of requesting the child

to repeat all or part of the erroneous utterance.

Confirmation questions: If the adult reply to the erroneous utterance was a

yes-no question pertaining to the linguistic content of the error-containing

utterance.

Move-on: If none of the other categories were applicable.

Negative evidence in language acquisition*

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